Ocular muscles related to a human's eyesight include ciliary muscles, rectus, iris muscles, etc. The eyesight may be protected or recovered by exercising such ocular muscles. In particular, the eyesight is closely related to the ciliary muscles. Here, the ciliary muscles are involuntary muscles that are not controlled by individual volition. However, when a focal distance of a lens in front of eyes is changed, the ciliary muscles unconsciously act in response to this change. Based on such characteristics of the ciliary muscles, there has been widespread a method of using a flipper to change the focal distance of the lens and thus improve the reactivity and strength of the ciliary muscles, thereby recovering the eyesight.
Such an exercising method using the flipper is inconvenient for a user since s/he has to repetitively and personally rotate the flipper at predetermined intervals.
To solve this inconvenience of using the flipper, there have been proposed many eyesight exercise devices for automatically changing the focal distance of the lens. However, these eyesight exercise devices have to include a plurality of lenses different in a diopter value from one another and thus have complicated inner structures. Besides, if the eyesight exercise device is used by a plurality of users who are different in eyesight from each other, they have to prepare separate eyepieces suitable for their own eyesight or use the eyesight exercise device while wearing glasses. Accordingly, it is difficult to generally use such a conventional eyesight exercise device.